Solute and Second Phase Evolution during Industrial Processing of AA3103

The complete evolution of solute content and second phases during full-scale industrial processing of AA3103 sheets has been measured. During pre-heating, dispersoids, which appear as plates or small polyhedra grow and the Mn solute content decreases. During subsequent breakdown rolling the dispersoid number-density increases significantly. The measured decrease of solute Mn after hot rolling and coil cooling is attributed to constituent particle growth, whereas the solute depletion during the final back-annealing is mainly caused by the growth of the dispersoids. These observations are compared to the predictions obtained by a semi-physical model for precipitation. Although simulations have been performed without any retro-fitting, for hot rolling the results compare quantitatively well with experiment, while for coil cooling and back annealing the modelled Mn solute depletion is underestimated. The precipitation process is found to be very sensitive to the microstructure, which illustrates the importance of coupling precipitation models with work hardening and softening models to obtain reliable predictions.

Cl− channels of the distal nephron

Cl− currents were observed under whole cell clamp conditions in cells of the rat cortical collecting duct (CCD), connecting tubule (CNT), and thick ascending limb of Henle's loop (TALH). These currents were much larger in intercalated cells compared with principal cells of the CCD and were also larger in the TALH and in the CNT compared with the CCD. The conductance had no strong voltage dependence, and steady-state currents were similar in inward and outward directions with similar Cl− concentrations on both sides of the membrane. Current transients were observed, particularly at low Cl− concentrations, which could be explained by solute depletion and concentration in fluid layers next to the membrane. The currents had a remarkable selectivity among anions. Among halides, Br− and F− conductances were only 15% of that of Cl−, and I− conductance was immeasurably small. SCN− and OCN− conductances were ∼50%, and aspartate, glutamate, and methanesulfonate conductance was ∼5% that of Cl−. No conductance could be measured for any other anion tested, including NO3−, HCO3−, formate, acetate, or isethionate; NO3− and I− appeared to block the channels weakly. Conductances were diminished by lowering the extracellular pH to 6.4. The properties of the conductance fit best with those of the cloned renal anion channel ClC-K2 and likely reflect the basolateral Cl− conductances of the cells of these nephron segments.

EFFECT OF SURFACE ROUGHNESS ON MASS TRANSFER IN A FLAT-PLATE MICROCHANNEL BIOREACTOR

Surface roughness exists in most microfluidic devices due to the microfabrication technique or particle adhesion. In this study, a numerical model based on Finite Volume Method has been developed to simulate the mass transfer in a flat-plate microchannel bioreactor with semi-circular protrusions uniformly distributed on the bottom. The results show that the mass transfer in rough channel is enhanced, as shown by lower minimum species concentration in the rough channel compared with that in smooth channel. Non-dimensional parameters such as Peclet number (Pe), Damkohler number (Da) and the roughness size ratio (β) can influence the effect of roughness greatly. However, it is important to ensure that the minimum species concentration in the rough channel is adequate for cell growth. The results would provide guidance on the perfusion requirements to avoid solute depletion or toxicity during cell culture.

The Mechanism of Intragranular Ferrite Nucleation on Inclusion in Steel

The intragranular ferrite, which renders fabrication of fine-microstructure and improves toughness of welds in ultra-fine grain steels, is often observed to nucleation on non-metallic inclusion. The mechanism of this nucleation is related to the interfacial energy between austenite, ferrite with inclusions, the solute depletion zone around the inclusions and the strain energy due to different thermal coefficients between matrix and inclusions, et al. The interfacial energy of iron with nitrides and carbides is crucial to promote the ferrite nucleation on such as VN. On the other hand, the composition change in local austenite is probably the control reason for ferrite on MnS and Ti2O3. The thermal strain energy is calculated to be far less than the driving force for phase transformation and not effective to promote ferrite nucleation unless at very small undercoolings.

Energy-filtered imaging of interfacial composition in complex Ni-base superalloys

In a wide variety of important engineering materials, including structural Ni, Fe, and Al-base alloys, the study of compositional gradients that occur at grain boundaries and other interfaces due to the precipitation of solute-rich second phases is of critical importance. X-ray spectrometry in the analytical electron microscope (AEM) has been used for many years to study solute depletion at interfaces in these alloys. It has been particularly effective at providing accurate, quantitative measurements in cases where the interface precipitates are spaced far apart and where relatively wide compositional gradients result from diffusion-controlled “collector-plate” mechanisms. However, in complex alloys, with heavy grain boundary coverage, multiple precipitate types, and/or multiphase matrices, x-ray microanalysis is more limited due to beam spreading and die associated 5-20nm spatial resolution achieved in these alloys with AEMs equipped with thermionic sources.Elemental mapping in an AEM equipped with an imaging energy-filter is an alternative method for the study of interface compositional gradients. It has been shown to be effective for this purpose in relatively simple situations in steels.